titter

Etymology 1

First attested in the 1610s. Probably from Middle English *titeren, *titren (attested in Middle English titering (“hesitation, vacillation”)), probably a frequentative of Middle English titten (“to waver”), related to Old Norse titra (“to shake, shiver, quiver”), dialectal Swedish tittra (“to snicker”).

verb

1. To laugh or giggle in a somewhat subdued or restrained way, as from nervousness or poorly-suppressed amusement.
   1863, Henry Wadsworth Longfellow, Tales of a Wayside Inn Part First: The Sicilian's Tale - King Robert of Sicily A group of tittering pages ran before.
   "Thou coxy, cackling candle!" said Catweazle. "Why dost thou titter?" 1971, Richard Carpenter, Catweazle and the Magic Zodiac, Harmondsworth: Puffin Books, page 70
   Nor had the joke been a vulgar one: it was the kind of elegant pleasantry that the minister of foreign affairs might have told the crown prince at a garden party a generation ago, causing the surrounding listeners to titter with delight. 1997, Haruki Murakami, translated by Jay Rubin, The Wind-Up Bird Chronicle, New York: Alfred A. Knopf, Inc.; republished New York: Vintage Books, 1998, page 363
2. (obsolete) To teeter; to seesaw.

noun

1. A nervous or somewhat repressed giggle.
   April 21, 1811, Samuel Taylor Coleridge, Table Talk There was a titter of […] delight on his countenance.

Etymology 2

Probably related to tit, titty.

noun

1. (slang, vulgar, chiefly in the plural) A woman's breast.
   Flesh Gordon 2 - I remember that this one was chock full of big titters. Many of them looked like the natural variety, as well. 21 February 1995, Agent_69 [username], “big breast video list”, in alt.sex.breast (Usenet)
   there was an old lady from raleigh who was so doggone nasty by golly just squeezin her titters you'd pick up some critters and bathe twice in one month for your folly 13 March 1999, MrMalo [username], “Re: State Capitals”, in alt.jokes.limericks (Usenet)
   “The poor dear, even her titters are weighted down with melancholy,” Pearle said to Mable. “I don't know what you're talking about. Her titters look perky enough to me,” Mable replied. 2013, Dorothy St. James, Oak and Dagger, Berkley Prime Crime